The present invention relates to a process for the preparation of coated textile fabrics with an aqueous dispersion of an organic binder in the presence of certain additives.
For the purposes of the invention, the term "coating" includes binding that requires complete impregnation of the textile fabric with the binder dispersion.
The production of coated textile fabrics, such as artificial leather, has long been known. One or more layers of the coating-agent are applied to the substrate using either a direct coating process or a transfer process. The coated textile fabrics may be used for the production of outer clothing, shoe upper material and linings, bag-making and upholstery material, tenting, tarpaulins, conveyor belts, and the like.
In the production of high quality coated textile fabrics, flexibility, tensile strength, and softness are, inter alia, of vital significance. Stiff fabrics are rejected by customers as uncomfortable.
It has been found important to avoid bonding fiber crossing points when producing flexible coated textile fabrics to avoid a loss of flexibility and the risk that the bond between the textile fibers and binder will be broken under flexural stress.
The undesired bonding of fiber crossing points may be avoided if the textile fabric is treated with aqueous dispersions of organic binders that are then coagulated. Coated textile fabrics produced in this manner are characterized by increased tensile strength and greater softness.
Various methods of coagulation are known, with the essential ones being the following:
(1) Bath coagulation, in which the substrate is coated with a binder dissolved in an organic solvent (for example DMF, DMSO, or THF) and the resultant product is passed through a bath of a non-solvent that is miscible with the solvent (for example, water). Coagulation occurs due to extraction of the solvent by the non-solvent. PA1 (2) Evaporation coagulation, which is based upon the use of a volatile solvent and a less volatile non-solvent for the binder. Under careful heating, the solvent is preferentially evaporated, so that the binder coagulates due to the constantly increasing proportion of non-solvent. PA1 (3) Salt coagulation, in which the coated substrate is introduced into a concentrated salt solution and the binder is coagulated by the high electrolyte content (i.e., it is virtually "salted out"). PA1 (4) The prepolymer method, in which a substrate coated with an isocyanate propolymer is immersed in water, thereby yielding a polyurea having a porous structure with elimination of CO.sub.2. PA1 (5) Coagulation by means of temperature increase, which is possible for heat-sensitive binders. PA1 (A) 100 parts by weight of a polymeric binder (calculated as solid) and PA1 (B) additives comprising, per 100 parts by weight of binder (A),
These methods have the disadvantage of requiring long periods for complete removal of the solvent, considerable effort for the separation and recovery of solvent and non-solvent, or the disposal of salt-laden effluents, or of giving results that are not always acceptable in terms of quality.
The object of the present invention was thus to provide a process for coating textiles without the stated disadvantages whereby a .,.high, quality product may be obtained using an aqueous dispersion and the lowest possible organic solvent content without the use of salt baths.
It has surprisingly been found that this object may be achieved by using an aqueous binder dispersion based on at least one polymer in the presence of certain additives.